Such devices comprise a vertical cylindrical tube supporting at its upper end the vise or the assembly platform and being guided for vertical movement within a guide tube. At its upper end the guide tube is axially slotted and can be clamped together to hold the support tube and therewith the vise or assembly platform in any desired vertical position. To this end a clamping device is provided which embraces the upper end of the guide tube and which can be connected to a work bench or the like. Normally the clamping device comprises two half-cylindrical shells which surround the upper end of the guide tube and which can be clamped together in order to decrease the diameter of said end. In order to facilitate the vertical adjustment a gas spring is provided which comprises a piston and cylinder unit and is arranged between the guide tube and the support tube and exerts an upwardly directed force on the support tube. In known devices of this kind the cylinder of the gas spring is arranged within and connected to the guide tube whereas the piston rod extending from the cylinder abuts the platform at the upper end of the support tube. Such device is f.i. disclosed in patent application Ser. No. 436,282.
Now it is often desirable to remove the vise or assembly platform from the work bench in order to have the work bench clear for other work. For this purpose one could screw the clamping device off the work bench which, however, is troublesome if the clamping device is connected by ordinary screws and not by an attachment screw. The other possibility is to loosen the clamping device so that the support tube with the vise can be pulled out of the guide tube. In this case, however, the piston rod still projects from the guide tube and disturbs working on the work bench.